Thousands of posters engaged in a vigorous debate over the catch, which some said was oversized and therefore illegal - but Green insisted was within the rights of recreational fishing in the state.

WA Fisheries regional manager metro Tony Cappelluti said his department and a shark scientist had assessed the pictures and decided not to prosecute, despite the shark being "close to the maximum size" allowed.

"We have now finalised our inquiry and there will be no action by the Department of Fisheries against Mr Green," he said.

"We agree that this shark is close to the maximum size, but there is insufficient evidence to conclusively determine its legal size."

WA regulations require the inter-dorsal fin measurement of a tiger shark to be no more than 700mm, measured from the front of the first dorsal fin to the point where the rear of the second smaller dorsal fin joins the shark's body.

One of the pictures posted shows Green lying alongside the shark, which appears to be almost identical to Green's stated height of 1.85m.

"The department's shark scientist has advised that a tiger shark would probably have to be over two metres in total length to have a 700mm inter-dorsal measurement," Mr Cappelluti said.